1. Field of the Invention
The present invention relates to a rotating disk type information storage apparatus including a magnetic disk apparatus, an optical disk apparatus and the like. More specifically, it relates to a mechanism structure for use in a positioning, in a high accuracy, of a head which writes/reads information on a predetermined position on a rotating disk in which the information is to be stored.
2. Description of the Related Art
In general, a rotating disk type information storage apparatus such as a magnetic disk apparatus includes a rotating disk in which information is to be stored, heads which write/read the information in this disk and an actuator for positioning these heads on a predetermined position on the rotating disk.
As an example, a structure of the magnetic disk apparatus will be described with reference to FIGS. 16 and 17. FIG. 16 is a top view of the conventional magnetic disk apparatus. FIG. 17 is a cross sectional view taken along line XVII--XVII of the conventional magnetic disk apparatus shown in FIG. 16. The shown apparatus has a magnetic disk 15 which has a magnetic film on the face surface thereof as the rotating disk, magnetic heads 31, each having an electromagnetic transducing element as the head, and a voice coil motor 142 which includes a permanent magnet 140 and a coil 141 as the actuator. The magnetic heads 31 are fitted to sliders 30 which function so as to float the magnetic head over a recording surface of the magnetic disk 15. The sliders 30 are also fixed and supported by gimbal plates 10 formed in load arms 12 which function so as to support the sliders. The load arms 12 are fixed to a pivot shaft 13 which stands upright on a base plate 19. The load arms 12 are held so that they can be rotated about an axis of the pivot shaft 13 within the surface parallel to the recording surface of the magnetic disk 15, that is, within the surface perpendicular to the pivot shaft 13.
A bearing 17 is put between the pivot shaft 13 and the base plate 19 so that the pivot shaft 13 can be easily rotated with respect to the base plate 19. A spacer 18 is fixed to the pivot shaft 13 in such a manner that a plurality of fixed load arms do not collide with each other. The coil 141 is provided in the position opposite to the load arms 12 so as to put the pivot shaft 13 between the spacer 18 and the load arm 12. When an electric current flows into the coil 141, an electromagnetic force is applied to the coil from the permanent magnet 140 which is fixed on the base plate 19 so that the coil may be intervened in the permanent magnet 140. The coil is rotated about the pivot shaft 13 together with the pivot shaft 13 within the surface perpendicular to the pivot shaft 13. The coil 141 and the permanent magnet 140 constitute the voice coil motor 142. The rotation of the coil 141 also causes the rotation of the load arms 12 fixed to the pivot shaft 13 about the pivot shaft 13, so that they perform an operation so as to position the magnetic heads 31 fitted to the sliders 30 on a predetermined position on the magnetic disk 15. Typically, in case of the magnetic disk apparatus using the magnetic disk which is 3.5 in. or less in an outer diameter thereof, a DC power source having a voltage of 12 V or less is used as a driving power source for use in the positioning operation described herein.
A high recording density is greatly required for such a rotating disk type information storing apparatus. one method of meeting this requirement is to reduce an error in the positioning of the write/read head on the rotating disk and thereby storing the information in a narrower region. In the magnetic disk apparatus shown in FIGS. 16 and 17, the positioning operation of the magnetic head on a magnetic disk surface is accomplished by a first actuator which consists of the voice coil motor 142. However, an improvement of positioning accuracy is limited in this method. Another method of accomplishing the higher-accuracy positioning operation is to mount a second actuator for finely adjusting the position of the magnetic head on a position thereof near the magnetic head.
FIG. 18 shows the structure of the actuator for finely adjusting the position of the magnetic head disclosed in Japanese Patent Unexamined Publication No. 62-250570. FIG. 19 is a cross sectional view taken along line XIX--XIX of the actuator shown in FIG. 18. The slider 30 which functions so as to float the magnetic head 31 is provided with a cantilever which includes a partial slider and laminated piezoelectric elements 400, 401, 402, 403, 404, each having a main component of oxide constituted of lead, zirconium and titanium (lead zirconate titanate: PZT). The magnetic head 31 is fitted to a tip end of this beam on a free end side thereof. At both the ends of respective piezoelectric elements are formed electrodes 502, 503, 504, 505, 506, 507 for applying the voltage to the piezoelectric elements. The electrodes 502, 504 and 506 are connected to an electrode 500. The electrodes 503, 505 and 507 are connected to an electrode 501. An application of the voltage to the electrodes 500 and 501 allows respective piezoelectric elements to be elastic. Thus, the cantilever comprising the piezoelectric elements and the partial slider is flexed. Therefore, the position of the magnetic head can be moved in a direction perpendicular to the axis of the cantilever beam. That is, this cantilever function of the actuator.
The actuator shown in FIGS. 18 and 19 is for positioning the magnetic head perpendicularly to a direction of movement of the load arm in a high accuracy. A change in an orientation of the piezoelectric elements and a part of the slider constituting the cantilever also allows the magnetic head to be relatively moved in a direction parallel to the direction of movement of the load arm shown in FIG. 16. The position of the magnetic head can be finely adjusted so that the error in the positioning provided by the voice coil motor may be corrected.
In such a manner, the use of the cantilever type actuator including the piezoelectric elements and a part of the slider permits the improvement of the positioning accuracy of the magnetic head. However, this actuator has three problems as described below.
A first problem is that a driving voltage is high. In case of the cantilever type actuator using the piezoelectric elements, in order to obtain the displacement of 1 .mu.m a high voltage is required as approaches scores of volts to 100 volts. However, as described above, in the magnetic disk apparatus using the magnetic disk having an outer diameter of 3.5 in. or less, the DC power source whose maximum voltage is 12 V is used so as to drive the voice coil motor for the positioning. Thus, in order to correct the positioning error of the order of 1 .mu.m caused by a positioning mechanism by the voice coil motor, another power source for the high voltage must be prepared. This is disadvantageous for a miniaturization and a cost reduction of the magnetic disk apparatus.
A second problem is that the magnetic head is vibrated during the positioning performed by the load arm. The magnetic head is mounted to the tip end on the free end side of the cantilever type actuator. Thus, when the load arm is moved with an acceleration by the positioning operation made by the voice coil motor, the force is applied to the tip end of the cantilever in a direction parallel to that of movement of the load arm. The force causes a vibration of the magnetic head. Since it takes a long time to stop the vibration, a necessary time becomes relatively longer for the positioning of the magnetic head on a predetermined position with high accuracy. This makes a problem large with respect to an increase of an information writing speed and an information reading speed of the magnetic disk apparatus.
A third problem is that a machining thereof is very difficult since a plurality of piezoelectric elements and electrodes must be fixed to one part of the slider having a length of 1 mm to a few mm. The actuator shown in FIG. 18 cannot be processed in a step of sequentially laminating piezoelectric films and electrode films on the surface of the slider. Thus, a member including a plurality of fine piezoelectric elements and electrodes of 1 mm or less in length is first formed. The member is then required to be fixed to a beam-shaped portion formed on the slider. Such a machining is far more complex than the process of laminating the films on a substrate for use in a semiconductor element or the like. This process is not suitable to a mass production. This makes a problem large as to the improvement of production efficiency of the actuator.